The long range objective remains the determination of the neuropsychologic factors which contribute to cardiac arrhythmias, while the specific focus is upon sudden death in patients with coronary heart disease. Laboratory and clinical components include investigation of 1) neural influences on ventricular vulnerability; 2) changes in cardiac excitability during different stages of sleep in animals and man; and 3) the influence of psychologic factors on ventricular vulnerability in normal animals and the occurrence of arrhythmias during myocardial ischemia. The effects of vagal stimulation on ventricular vulnerability, alone and in combination with sympathetic stimulation, will be examined in the anesthetized dog. Changes in myocardial excitability will be correlated with specific sleep stages. The influence of various psychologic stressors on the occurrence of arrhythmias will be examined in coronary occluded dogs and patients with ischemic heart disease.